Stirring mill

ABSTRACT

Stirring mill with a grinding container filled with milling pellets approximately 0.078 inch to 0.236 inch in size and equipped with a rapidly running stirring mechanism where a pump feeds in at one end the material to be ground and the ground material leaves the container at the other end by way of a separating arrangement that separates the grinding container from the discharge space and the milling pellets and the coarse components from the fine material, having a top portion connected with the grinding container that defines the discharge space and which has a material discharge duct the height and/or width of which is adjustable and a pressure head duct.

llite States Patent Engels 1 Mar. 2, W72

[54] STIRRlNG MlLL 3,337,140 8/1967 Wahl ..241/172 11 3,352,500 11 1967 Molls et al. [72] Inventor: Kaspar Engels, Mannheim, Germany 3,450,356 61969 Szegvari ..241/172 [73] Assignee: Firms Draiswerke GmbH, Mannheim- Waldhof, Germany Primary Examiner-Granville Y. Custer, Jr. [22] Filed D 5 19 Attorney--Robert H. Jacob 211 Appl. No.: 882,430 [571 Stirring mill with a grinding container filled with milling pel- 152 11.5. at ...,241/172, 241/180 vv d i inch inch in size and 151 1111. ctm. "802a 17/16 equip? with a rapidly stirring a 581 Field oifienrch ..241/171 172 173 180 181 feeds in end material be gm'md and ground material leaves the container at the other end by way 56 R Cited of a separating arrangement that separates the grinding con- 1 e erences tainer from the discharge space and the milling pellets and the UNITED STATES PATENTS coarse components from the fine material, having a top portion connected with the grinding container that defines the 3,486,705 12/1969 Szegvari ..24l/l72 discharge Space and which has a material discharge duct the 21 1 2512 3 8 :2 height and/or width of which is adjustable and a pressure head y C O d t 3,243,128 3/1966 Tight ..24l/l72 X 3,311,310 3/1967 Engels et al ..241/l72 X 3 Claims, 2 Drawing Figures srnmmo Mitt.

BACKGROUND OF THE INVENTION The present invention relates to stirring mills. More in particular, the invention is concerned with stirring mills of the type having an erect or upright grinding container which is filled with very small grinding pellets which are kept in motion by a high speed stirring mechanism. The material being ground which passes through the grinding container carries along the grinding pellets so that a separating arrangement is needed proximate the discharge outlet of the mill.

Stirring mills having an open grinding container or drum involve a particular disadvantage in that they develop Whirlpools in whose area the stirring tools partly run freely and, together with the grinding pellets, undesirably work air into the material being ground so that an interfering foam formation develops. If viscous or pasty milling material is supplied to open mills, there develops considerable carrying along of grinding pellets to the separating chamber that is primarily constituted by screens, and this results in clogging of the screen and overflowing of the grinding container. If for that reason the load of the grinding container is reduced, the grinding output is decreased, which results in agglutination at the screens.

ln known stirring mills, there further arise difficulties in sealing the shaft of the stirring mechanism with respect to the grinding container. Particularly due to the wearing effect of the mixture of the material being ground and small milling pellets, the bearings of the stirring shaft and the seals are rapidly destroyed. It is, therefore, necessary to exchange the bearings and seals at short intervals. For sealing, for example, two stuffing boxes or glands are required. With closed stirring mill mechanisms, it is further not possible to have an optical control of the conditions in the grinding container, and it is not possible to finely control the manner of operation of the mill. No control can be introduced to determine whether the whirlpooling which is responsible for the working in of air has been eliminated. If the outlet pressure of the ground material is too low, then the suction effect of the whirlpool resulting from the centrifugal forces can result in sucking air into the mass of treated material through the stuffing boxes that are very susceptible to leakage in these mills. Where the pressure on the material being ground is too high, the stuffing box is unnecessarily placed under a load.

SUMMARY OF THE INVENTION It is therefore an object of the invention to provide a stirring mill that avoids the shortcomings of the known open and closed stirring mills and which can satisfactorily operate without any particular stuffing box seal for the stirring shaft. It is furthermore an object of the invention that the mill operate under a small excess pressure against the atmospheric pressure and that it is finely controllable.

The invention is considered to be inherent in a stirring mill comprising a grinding container filled with grinding pellets of a magnitude of 0.078 inch to 0.236 inch equipped with a rapidly operating stirring mechanism supplied with material to be ground by a pump at one end, and from which the finely ground material departs at the other end by way of a separating arrangement, which divides the grinding container from the discharge chamber, as well as the grinding pellets from the coarse components and from the finely ground material, and in which the discharge space is defined by an added chamber in the form of a super-structure connected to the grinding container which has a discharge outlet that is adjustable in height and/or width and a pressure head duct.

In accordance with the invention, cylindrical screens or flat screens may be utilized as separating devices. The separating arrangement separates the grinding container from the discharge space, while the discharge space is defined by a superimposed chamber in which the finely ground material accumulates before reaching the outlet and develops a back pressure toward the grinding container. Accordingly, it is accomplished that the grinding container is completely filled and no air current formation is possible in the grinding container. The result is an improvement of the degree of effectiveness of the mill to which is also added the pressure that acts on the material being ground in the container during the working operation. In accordance with one feature of the invention, a superstructure in the form of an added chamber is arranged upon the upright or erect open stirring mill upon the grinding container which has a pressure head duct that surrounds the grinding shaft in the area of the discharge chamber, and where between the pressure head duct and the added chamber a separating means is provided. The pressure head duct which is connected with the screen encompasses the drive shaft of the stirring mill relatively narrowly over a predetermined distance, while the annular gap between the drive shaft and the pressure head duct may be free of any seal or stuffing box. The wall of the additional chamber or reservoir is extended beyond the separating arrangement so far that above the separating arrangement or means there is formed a level of ground material at the height of the discharge space which is sufficient to form a free space in the area of the grinding container or within and below the separating zone and thus prevent a decrease of the grinding efiect and/or air suction. For alternating conditions of operation a ground material discharge arrangement is provided for continuously varying the level of the ground material in the discharge space. In an advantageous manner, discharge apertures can be provided that may be optionally used in different levels of height in the added chamber or an outlet may be used, the height of which is continuously or uninterruptedly adjustable. In accordance with a particularly simple improvement, an up and down flexible discharge hose may be connected to an outlet of the superimposed reservoir which is suspendable by means of supporting elements such as a hose support, a suspension strap and suspension hooks at the desired height for the level of the material being ground.

In an erect or upright grinding mill having a cylindrical screen, the pressure head duct of the superstructure may connect with the upper brim of the screen, while the grinding shaft is freely journalled at its upper end outside the superstructure, and it possesses no stirring elements in the area of the superstructure. Due to the cylindrical screen, there results a screen space of particularly large surface area, if the diameter of the cylindrical screen corresponds to the diameter of the grinding container or is designed for its order of magnitude.

The pressure head duct extends beyond the upper edge of the cylindrical screen. This results in safeguarding against the overflow of the mill when improperly operated. Due to the design of the outlet stud with an overflow are or knee that is adjustable as to height, a finely adjustable pressure head on the grinding container is obtained, while the material in the pressure head stub may rise. The outlet stud of the superstructure or added chamber is located above the upper edge of the cylindrical screen so that the screen is continuously immersed in the material being ground, and there need be no concern about drying or the like resulting in gobbing of the screen. Accordingly, the mill may be shut down without damage for longer periods of time, for example during the night, without it becoming necessary that the screen has to be cleaned before the mill is again put in operation. The free area of the added chamber without stirring elements or arms provides the advantage that the formation of air pockets is avoided to a great extent. The further condition that the ground material disposed in the added chamber has an increased number of ground pellets dispersed therein which together with the resistance of the screen oppose the formation of air pockets in the rotating ground material also provides advantageous effects. In the area of the added chamber no noticeable air intake occurs. The liquid level in the pressure head and in the added chamber can be examined from the top by unobstructed visual control. Furthermore, the indication of the material level can be efiected through viewing glasses, floats, feelers, sensors or the like.

BRIEF DESCRIPTION OF THE DRAWINGS Further advantageous features of the invention will become apparent from the following description with reference to the embodiments illustrated in the drawings where corresponding reference numerals identify equal parts and in which FIG. 1 illustrates in section an embodiment of the invention where different closure valves determine the discharge level of the ground material, and

FIG. 2 shows an embodiment of the invention in section that utilizes a discharge hose the height of which is adjustable.

DESCRIPTION OF THE INVENTION The stirring mill comprises a grinding container 1 filled with small grinding pellets 1a, which for cooling or heating is equipped with an outer wall 2. A stirring shaft 5 having stirring members 6 driven at high velocity extends into the grinding container freely floating in the bearings 3, 4. The stirring members are in the form of solid disks. The material to be ground is forced into the grinding container by means of a feed pump 7 through intake or inlet 8. The finely ground material leaves the grinding container 1 by way of a separating or dividing means 9 that holds back the components of coarse material and the grinding pellets. The separating means furthermore divides the grinding container 1 from a discharge space or reservoir 10. The discharge space 10 is arranged in a superstructure or top 11 that is connected with the grinding container. This top structure has a material discharge outlet 12 and central tubular member 13 affording a pressure head duct 13.

In accordance with FIG. 1, the stirring mill is in upright position with the superstructure and the pressure head duct 13 open at the top. The separating or dividing means is a flat screen 9 between the pressure head duct and the upper border of the grinding container. In the superstructure discharge ducts 12 that can be closed by valve 14 may be optionally disposed at different levels of height in order to enable adjusting the level 15 of the liquid screened material to different heights in the reservoir 10. The pressure head duct 13 encompasses the shaft 5 with a relatively narrow gap 16 therebetween, in which connection the level 15 of the material being ground between shaft 5 and pipe 13 is higher than the level 15 of the ground material as determined by the resistance of the ground material in passing through the screen 9. In the area of the superstructure 1 1, the shaft has no stirring elements and the formation of air pockets in the grinding container and in the discharge space or chamber 10 is avoided. In the embodiment in accordance with FIG. 1, the ground material may enter into the space between the shaft 5 and pipe 13. Since, however, no vertical flow of liquid takes place in this space after the mill has been filled, no accumulation of grinding pellets need be expected in the gap 16. If at the beginning of the grinding process, grinding pellets should enter the gap 16 between pipe 13 and shaft 5, then these grinding pellets will sink down again upon attainment of constant operating conditions. Even with liquids that form foam, the quantity of air worked into the annular space 16 between shaft and pipe is negligible. The foam that may develop under certain conditions can be drawn out of tube 13.

The superstructure or top 11 in accordance with FIG. 2 has an outlet 12 to which an elastic hose 17 is connected that can be suspended at different heights or levels by supporting elements such as a hose clip 18, a strap 19 and the supporting hook 20 whereby the level of the ground material in the discharge chamber 10 is adjustable. The separating means 9 is again in the form of a screen which in this embodiment is a cylindrical screen.

At the upper border of the cylindrical screen the pressure head duct is connected. The pressure head duct may be connected with the superstructure by means of struts 21. The outlet 12 is arranged at such a level in the superstructure 11 that the cylindrical screen 9 is disposed below the level of the ground material 15 and, therefore, is not able to dry. In-

asmuch as no stirring elements are provided in the area of the superstructure, there results a quiet operating condition in that area of the ground material, which avoids any pronounced whirlpooling of liquid material around the unbladed upper portion of the shaft 5 and consequent entry of air into the ground material. The distance between the pressure head duct 13 and the shaft 5 is relatively large here so that pressure of grinding pellets between shaft and pipe are safely avoided. Furthermore, only minor differences in velocity can arise in the mix of grinding pellet and ground material in the region of the cylindrical screen, which practically precludes the working in of air if foam should form. Finally, the danger of overflow of the mill is almost precluded.

Having now described my invention with reference to the embodiments illustrated, what I desire to protect by letters patent is set forth in the appended claims.

I claim:

1. In a stirring mill of the type comprising an upright, open top grinding container and a screening device for liquid material which is forced upwardly therethrough, the combination of a high speed rotary shaft depending into said grinding container and having a lower portion therein equipped with stirring blades and an unbladed upper portion extending upwardly beyond said screening device; and a superstructure over said grinding container comprising a central tubular member surrounding said unbladed shaft portion in radially spaced relation thereto and communicating at its lower end with said grinding container; a peripheral outer wall portion spaced radially from said tubular member and extending upwardly above said screening device so as to provide a reservoir for the accumulation of liquid screened material therein, outlet passage means for said reservoir including adjustable overflow control means operable to selectively maintain a liquid head of predetermined height in said reservoir whereby a liquid head of increased height will be caused to accumulate within said tubular member and prevent whirlpooling of liquid material around said unbladed shaft portion, and said screening device comprising a screen extending between the lower end of said central tubular member and the proximate upper end of said grinding container.

2. A stirring mill as set forth in claim 1 wherein said screening device is a screen cylinder and the diameter of said screen cylinder substantially equals the diameter of said grinding contamer.

3. A stirring mill as set forth in claim 2 wherein a ground material discharge stud is connected to said reservoir on a level above the upper edge of said screen cylinder. 

1. In a stirring mill of the type comprising an upright, open top grinding container and a screening device for liquid material which is forced upwardly therethrough, the combination of a high speed rotary shaft depending into said grinding container and having a lower portion therein equipped with stirring blades and an unbladed upper portion extending upwardly beyond said screening device; and a superstructure over said grinding container comprising a central tubular member surrounding said unbladed shaft portion in radially spaced relation thereto and communicating at its lower end with said grinding container; a peripheral outer wall portion spaced radially from said tubular member and extending upwardly above said screening device so as to provide a reservoir for the accumulation of liquid screened material therein, outlet passage means for said reservoir including adjustable overflow control means operable to selectively maintain a liquid head of predetermined height in said reservoir whereby a liquid head of increased height will be caused to accumulate within said tubular member and prevent whirlpooling of liquid material around said unBladed shaft portion, and said screening device comprising a screen extending between the lower end of said central tubular member and the proximate upper end of said grinding container.
 2. A stirring mill as set forth in claim 1 wherein said screening device is a screen cylinder and the diameter of said screen cylinder substantially equals the diameter of said grinding container.
 3. A stirring mill as set forth in claim 2 wherein a ground material discharge stud is connected to said reservoir on a level above the upper edge of said screen cylinder. 